1. Field of the Invention
The present invention relates to a memory device and a method of fabricating the same, and more particularly, to a charge trap memory device using a composite of nanoparticles and a method of fabricating the charge trap memory device.
2. Description of the Related Art
Non-volatile memory devices are a data storing device that can retain stored data without loss even when the supply of power is interrupted. Flash memory device are a representative example of non-volatile memory device.
Flash memory devices can be classified into either floating gate memory devices in which charges are accumulated in a floating gate formed between dielectric layers and charge trap memory devices in which charges are accumulated in a charge trapping layer that is formed between dielectric layers and acts as a storage node.
An example of a charge trap memory device includes a silicon-oxide-nitride-oxide-silicon (SONOS) memory device using a silicon nitride layer as the charge trapping layer. The SONOS memory device has a structure in which a tunnel insulating layer, a charge trapping layer, and a blocking insulating layer are sequentially stacked on a silicon substrate in which source and drain regions are formed, and a gate electrode is formed on the blocking insulating layer. The tunnel insulating layer and the blocking insulating layer may be formed of SiO2, and the charge trapping layer may be formed of a silicon nitride (Si3N4) layer.
A charge trap memory device using nanoparticles as the charge trapping layer have been vigorously researched in recent years. Metal and semiconductor nanoparticles have large work functions and can stably store electrons transported from an electrode, and thus can serve as trap sites storing charges passing through the tunnel insulating layer.
In order to satisfy the requirement for flash memory devices having larger memory capacity that increases annually, the sizes of memory cells rapidly decrease. In addition, in charge trap memory devices, many efforts have been devoted to the manufacture of a flash memory device that can store charges while remaining data stored by a leakage current for a long time and that has smaller memory cells. Thus, it is likely to implement a highly integrated memory having very small memory cells using a single nanoparticle as a separate memory cell.
However, when more nanoparticles are used in a unit area in order to increase the integration density of memory, due to the increasing of charge accumulated in the nanoparticles, the speed and performance of the memory are improved. However, as the density of nanoparticles increases, the distance between the nanoparticles becomes shorter, thereby increasing a leakage current to the tunneling between the nanoparticles. A larger leakage current leads to shorter information retention time and poor memory performance. In addition, a higher density of nanoparticles leads to the agglomeration of the metal nanoparticles in a memory manufacturing process and lowers the performance of the memory device.